Milling tool

ABSTRACT

The invention relates to a milling tool made of cemented carbide having a cylindrical shank ( 16 ) and a cutting head ( 18 ) for the face milling of workpieces made of a hard-brittle material. The cutting head ( 18 ) is configured as an end mill with corner radius or a ball nose end mill having a cutting length (L  2.2 ). The shank ( 16 ) has, up to its chucking end ( 26 ), at least one clearance segment ( 28 ) having a smaller diameter (d 3 ) than the cutting head ( 18 ). The tip of the cutting head ( 18 ) is coated or tipped with hard mineral along a length (L 2 ) having a diameter (d 1 ) used for finishing, to which is connected a segment ( 24 ), which is used for roughing, having the cutting length (L 2.2 −L 2 =L 2.1 ) and a reduced diameter (d 4 ), which is smaller than the diameter (d 1 ) of the cutting length (L 2 ) on the cutting head ( 18 ) used for finishing and is greater than the diameter (d 3 ) of the clearance segment ( 28 ).

The invention relates to a milling tool made of carbide having acylindrical shank and a cutting head for the face milling of workpiecesmade of a hard-brittle material according to the preamble of claim 1.

In the milling processing of workpieces made of very hard material, themilling tools used for this purpose are subject to great wear. Thisproblem also occurs, in particular, in the profile machining ofworkpieces made of graphite, in order to produce from it, for example,electrodes for spark eroding, which are used for CNC machines. Thegraphite block used as the starting material is normally machined usingan end mill made of cemented carbide, the cutting head of which can becoated or tipped with diamond.

A milling tool having the features of the preamble of claim 1 is knownfrom EP 2 540 427 of the applicant. There, the cutting head is suitableonly for finishing due to its small coated length, which permits only ashort feed, but not for roughing. The adjoining length of the shaft isconfigured as a clearance segment and thus is not cutting, so that it isavailable neither for roughing milling nor for finishing.

Another milling tool, which has the features of the preamble of claim 1,is described and illustrated in DE 10 2006 026 851. However, also inthis, a non-cutting clearance segment directly adjoins the head segment,which is used for finishing, so that two differently-configured millingtools have to be kept available and used for roughing and finishing.

The same also applies to a milling tool according to WO 2018/163148, thecutting region of which is also suitable either only for roughing oronly for finishing.

The object underlying the invention is to configure a milling tool sothat it can be used both for roughing and for subsequent finishing of aworkpiece.

The solution to this problem results from the characterizing features ofclaim 1, according to which a segment, which enables a roughing, isconnected to the short cutting length of the cutting head that is suitedfor finishing. Due to its set-back diameter, the clearance segmentprevents the undesired pressing in the radial direction during thefinishing after the roughing.

In an advantageous development of the invention, both the finishingsegment and the roughing segment of the cutting head are coated ortipped with hard mineral, in particular diamond.

The invention is explained below with exemplary embodiments, which areillustrated in the drawings.

FIG. 1 shows the schematic illustration of a workpiece to be machined,for example, an electrode for spark eroding, using an end mill or a ballnose end mill,

FIG. 2 shows the view of an end mill with corner radius having a coatedcutting head according to the prior art,

FIG. 3 shows, in a variant of FIG. 2, a known end mill with cornerradius having a non-cutting clearance,

FIG. 4 shows the view of a milling tool according to the invention and

FIG. 5 shows a cutout enlargement of the cutting head in the region V ofFIG. 4.

FIG. 1 schematically shows the view of a workpiece 10 made of ahard-brittle material, for example graphite, the conical upper part 12of which is to be machined in order, for example, to produce anelectrode for spark eroding. In order to produce the desired profile ofthe upper part 12, a milling tool, designated overall by 14, is used,which has a cylindrical shank 16 and a ball nose-shaped cutting head 18here. During the machining, the milling tool 14 rotates around itslongitudinal axis 22 and simultaneously moves along the profile of theworkpiece 10 around its longitudinal axis 20. For the machining of theconical upper part 12, the milling tool 14 is moved both in thex-direction and in the z-direction, optionally also in all three axes x,y and z.

FIG. 2 shows a schematic view of a conventional milling tool 14, whichis configured here as an end mill with corner radius. As is known fromEP 2 540 427 B1 of the applicant, the cutting head 18, which is providedat the tip of the shank 16 having the diameter d1, has a length s thatconsists of the radius r of the edge rounding and a short additionallength a. The cutting head 18 has, in the height s, i.e. at thetransition to the shank 16, the same diameter d1 as the shank 16. Thishas the consequence that, with progressive feeding of the milling tool14 in the axial direction z (see FIG. 1) during roughing and finishing,the non-cutting shaft 16 is subjected to radial compressive loads andthus deformations, which not only affects the milling accuracy but canalso lead to a fracture of the shank 16.

The improved configuration of the milling tool 14 according to EP 2 540427, which is shown in FIG. 3, brings about a certain remediation here,because there the shank 16 has a smaller diameter d3 than the cuttinghead 18, which projects radially beyond the shank 16, in height s. Inthis way, a non-cutting clearance 28 is formed up to the chucking end 26of the milling tool 14, so that no radial compressive forces aregenerated during roughing or finishing. These occur only when the bladediameter d1 gradually decreases when the milling tool 14 is axially feduntil it reaches the dimension d3, so that the non-cutting longitudinalregion of the clearance 28 causes a radial pressing.

The design of the cutting head 18 of the milling tool 14 according tothe invention results from FIGS. 4 and 5. In particular, FIG. 5 showsthat the cutting head 18 has, at its tip, a cutting region having thelength L2 and the diameter d1, which is used for finishing a previouslyroughened upper part 12 of a workpiece 10 (cf. FIG. 1). The length L2corresponds to the maximum feeding of the milling tool 14 during thefinishing.

At point W1, the cutting head 18 transitions into the segment 24 havingthe length L2.2−L2=L2.1, the diameter d4 of which is somewhat (forexample, approximately 0.05 mm) smaller than the diameter d1 of thecutting region L2. According to the invention, the segment L2.2−L2=L2.1is configured in a cutting manner and is used for roughing milling ofthe workpiece.

Only at the circumference W2, a vacant, non-cutting clearance segment 28having the once more reduced diameter d3 extends over the length L3−L2.2of the shaft 16 up to the beginning of the chucking end 26. The chuckingend 26 then has an identical or somewhat larger diameter d2.

Both the cutting head 18 and the roughing segment 24 can be coated withhard mineral, for example diamond, over their length L2 or L2.2−L2=L2.1.

1. Milling tool made of cemented carbide, having a cylindrical shaft(16) and a cutting head (18) for the face milling of workpieces made ofhard-brittle material, wherein the cutting head (18) is configured as anend mill with corner radius or a ball nose end mill having a cuttinglength, and the shank (16) has, up to its chucking end (26), at leastone clearance segment (28) having a smaller diameter (d3) than thecutting head (18), characterized in that the tip of the cutting head(18) is coated or tipped with a hard mineral along a length (L2) havinga diameter (d1) that is used for finishing, to which is connected asegment (24), which is used for roughing, having the cutting length(L2.2−L2=L2.1) and a reduced diameter (d4), which is smaller than thediameter (d1) of the cutting length (L2) on the cutting head (18) usedfor finishing and is greater than the diameter (d3) of the clearancesegment (28).
 2. Milling tool made of cemented carbide according toclaim 1, characterized in that the cutting length (L2.1) used forroughing is also coated or tip with hard mineral.